This invention relates to contact electrodes for microdevices, and their method of manufacture.
Microelectromechanical systems (MEMS) are very small moveable structures made on a substrate using lithographic processing techniques, such as those used to manufacture semiconductor devices. MEMS devices may be moveable actuators, valves, pistons, or switches, for example, with characteristic dimensions of a few microns to hundreds of microns. A moveable MEMS switch, for example, may be used to connect one or more input terminals to one or more output terminals, all microfabricated on a substrate. The actuation means for the moveable switch may be thermal, piezoelectric, electrostatic, or magnetic, for example.
The MEMS switch may, for example, include a set of gold electrodes formed on the end of a cantilevered beam, which may make electrical contact with another set of conductive electrodes when the beam is actuated by, for example, thermal or electrostatic displacement. Because of the small size of the device, the forces involved in these actuation mechanisms may not be substantial. In addition, because of the small contact area of the electrodes, the electrical contact may be dominated by a very small portion of the electrode surface, for example one or two gold grains. Any event which causes a change to this portion of the electrode surface, such as deformation or contamination, can lead to a large change in the contact resistance between the electrodes. A variable, and particularly an increasing contact resistance can cause a substantial reliability issue with the switch, especially when the contacts are transmitting an electrical signal which is diminished by increased contact resistance, or a current-carrying switch which generates more heat when the contact resistance rises. For at least these reasons, in general, a low contact resistance is a figure of merit for both MEMS and non-MEMS electrical switches.